The CFRBCS has collected baseline epidemiological and clinical data. The ability to follow-up a large cohort of "at risk" individuals was a key feature of the establishment of the CFRBCS. It is proposed to conduct a five year follow-up survey of all 20,000 consenting individuals (8,000 affected) recruited into the CFBRCS, so as to form a prospective cohort study of cancer families. We plan to systematically collect updated epidemiological , reproductive, lifestyle, prevention, family history and outcome information. For individuals who have been diagnosed with breast or ovarian cancer, pathology material, cancer verification and treatment details will be sought. By the nature of recruitment, being targeted towards individuals from multiple-case families, or women with breast cancer diagnosed at a relatively young age and/or with a family history of the disease, this cohort will be enriched for individuals for individuals who carry a genetic risk of breast cancer. The follow-up data will be essential for several Scientific Modules included in this collaborative UO1 application, and provide data that would be used to address prospectively the hypothesis of the other modules. Even within 5 years, there should be sufficient new cases among women unaffected at baseline to address some key issues about genetic and environmental risks of breast cancer. The potential for answering questions using the CFRBCS will be enhanced by new collaborations with other family-based follow-up studies: A European-based study of BRCA1 and BRCA2 mutation carriers, an Australian study of multiple-case families which uses the CFRBCS questionnaires. This proposal represents a window of opportunity to institute prospective follow-up of the cohort, as recruitment has occurred relative recently. Establishment of systematic follow-up is essential if we are to reap the full reward from the enormous investment in time, money, resources, and of critical importance the goodwill and co-operation of study participants, in being able to address the questions for which the Registry was established to answer.